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Adults over age 50 years, on average, lose 1% to 2% of muscle mass and 3% to 4% of muscle strength per year. This is due to reductions in neuronal, neuromuscular, and muscle function.

Sarcopenia (age-related muscle atrophy) and dynapenia (age-related muscle weakness) are defined inconsistently among scoring systems and clinical guidelines using aspects of (1) physical function (ie, gait speed), (2) muscle strength, and (3) muscle mass; thus there is no uniform diagnosis accepted for these conditions at the present time. However, if progress is to be made regarding lifestyle and pharmacologic interventions, a uniform definition is essential.

Age-related changes in cartilage, tendons, and ligaments contribute to common arthritic syndromes (eg, osteoarthritis and a general decline in joint range of motion with age, but the mechanisms that are age) versus disease-related have not been clearly elucidated.

Intervertebral disk degeneration increases with age, with at least some degree of degeneration universally present by the sixth decade of life. However, the presence of disk degeneration does not correlate well with symptoms of pain, so it is difficult to determine the clinical significance of these findings.

There are a large number of age-related changes that occur in the tissues that make up the musculoskeletal system. Many of these changes contribute to the most pervasive chronic conditions seen in older adults. In fact, musculoskeletal disorders are the most common cause of chronic disability in late life. This is attributable both to the prevalence of disorders affecting the musculoskeletal system as well as the central role of the musculoskeletal system for daily function for independent living. Despite the prevalence of musculoskeletal disorders, however, there is still much to learn about the pathogenesis of these disorders, including the role of aging, and the interactive role of physical inactivity, in their development.

This chapter reviews aging in each of the major components of the musculoskeletal system including the neuromuscular system, which includes a detailed discussion on sarcopenia (age-related muscle atrophy) and dynapenia (age-related muscle weakness), as well as cartilage, ligaments and tendons, and intervertebral disks (refer to Table 113-1). Although bone is a key player in the musculoskeletal system, aging changes in this tissue are discussed in more detail in Chapter 118.